Vehicles, trains and planes are equipped with seats in which passengers can travel harnessed/belted or unharnessed/unbelted during at least a part of a journey. These seats are typically provided with a number of safety features which are designed to reduce injury to a seated individual when the vehicle, train or plane, hereinafter referred to as the transportation mode, either makes a sudden change in speed and/or is involved in a collision. For example, it is known to equip such seats with safety belts. The safety belts are provided generally in one of two forms, firstly there is a lap belt which is characterised by having 2-points of attachment and a single strap which is arranged so as to pass across the pelvis of a seated individual; secondly, there is a 3-point safety belt which is characterised by having 3-points of attachment and a strap which is arranged to pass across the torso of a seated individual as well as across the pelvis.
It is known that where a transportation mode has to brake suddenly or is involved in a collision, individuals are typically thrown forward within their seats. The aforementioned safety belts serve to limit this forward movement and so effectively restrain an individual in a given seat. The effectiveness of this restraint is determined by the nature of the safety belt system (system is defined as the integration as a whole of the seat belt, its anchorage point, the integration of the anchorage to the seat structure, and finally, the attachment of the seat assembly to the transport mode structure). For example, in a extreme situation where an individual is not wearing a safety belt, during deceleration, the individual is blown to be thrown forward and the knees of such an individual make contact with the lower rear part of a forward seat and then the upper torso/head of such an individual makes contact with the upper rear part of the same seat. In the instance where a lap belt is used, when the individual is thrown forward, the knees of the individual go forward to a lesser extent, compared to that of an unbelted individual, but the upper torso/head of such an individual is thrown rearward and then thrown forward with a considerable rotational force often resulting in a condition known as whiplash. In the instance where an individual is wearing a 3-point seat belt the amount of forward movement of the upper and lower part of the body is considerably reduced by the restraining effect of the seat belt system and thus the amount of damage to such an individual is minimised.
In addition, in so far as vehicles are concerned they are classified within the European Community System according to their seating capacity and general size. For example, M1 type vehicles are vehicles with less than 8 seats plus the driver. These would normally be cars weighing between 1 and 2 tonnes and in these vehicles the lap belt test load is 22,250.+-.200 Newton.times.20 g.
M2 vehicles are vehicles with more than 8 seats plus the driver and having a maximum weight of less than 5 tonnes. The lap belt test load for these vehicles is 11,100.+-.200 Newton.times.10 g. This would normally be a van derived mini-bus weighing 2.5 to 5 tonnes.
A M3 type vehicles is a vehicle with more than 8 seats plus driver and weighing more than 5 tonnes. The lap belt test load for these vehicles is 7,400.+-.200 Newton.times.6.6 g.
It can therefore be seen that the lap belt test load increases as the size of the vehicle decreases. This is because, as the weight of the vehicle decreases the deceleration rate increases and thus the force with which an individual is thrown forward increases.
It therefore follows that the structural characteristics of a seat determine not only whether an individual can be sufficiently restrained in a given safety belt during impact but also the extent to which an individual in a rear-most seat will be damaged following impact with the rear of a foremost seat.
We have conducted investigations in order to determine the most desirable properties of a safety seat with a view to ensuring that a seated individual is suitably restrained using a safety belt during impact and that a rearward individual colliding with the rear of the seat suffers minimal damage or at least recommended levels of injury criteria are met.
Recommended levels of injury are as defined in United Nations document ECE R80 Annex 7 at a seat pitch of 750 mm and a sled pulse of 12 g. These being:
(HAC) HEAD ACCEPTABILITY CRITERION less than 500 as per Section 5.2.2.1.1.
(ThAC) THORAX ACCEPTABILITY CRITERION less than 30 g for up to 3 ms as per Section 5.2.2.1.2.
(FAC) FEMUR ACCEPTABILITY CRITERION less than 10 KN(8 KN for more than 20 nms) as per Section 5.2.2.1.3.
We have therefore endeavoured to provide a safety seat which can absorb dynamic energy and which can absorb resistance to applied loading.
Our safety seats have essentially 3 functions. Firstly, the seat is sufficiently strong to withstand maximum loading which is typically applied to such a seat during a collision. Secondly, it has deformable and/or collapsible properties during collision and, thirdly, it has suitable energy absorbing capacity during collision so as to protect an individual seated rearward of same.
It is therefore an object of the invention to provide a safety seat which minimizes damage to an individual seated rearward thereof during collision.
It is a further object of the invention to provide a safety seat which suitably restrains a seated individual during collision.
It is a further object of the invention to provide a safety seat which undergoes deformation and/or collapse in a relatively controlled fashion during collision.